In view of what he [Moseley] still have accomplished … his death might well have been the most costly single death of the War to mankind generally – Isaac Asimov
The First World War was one of the most deadly and wasteful conflicts in human history. An entire generation torn apart, and many brilliant minds lost. Who knows what Wilfred Owen might have gone on to achieve, had he not been killed in action almost exactly a week before the armistice? And he was just one among many. But while most people have heard of Wilfred Owen, many of you reading this may never have heard of Henry Gwyn Jeffreys Moseley.
Henry Moseley, known to his friends as Harry, was born in 1887. His father was a professor of anatomy and physiology at the University of Oxford, and his mother, herself the daughter of an eminent biologist, went on to become the British women’s chess champion in 1913. So it’s hardly surprising that Harry excelled at science, winning the physics and chemistry prizes at Eton where he had been awarded a King’s scholarship. What is perhaps more surprising is that Harry did not follow the family tradition and go into biology – his interests lay in chemistry and physics, and particularly in the structure of the atom.
After graduating from Trinity College, Oxford, Harry Moseley went to Manchester to work under Sir Ernest Rutherford, one of the most eminent scientists of the time, who was studying radioactivity. In 1913 Rutherford offered Harry a fellowship, which he declined, preferring to return to Oxford where he could work on his own independent research. In particular he wanted to work on solving the problem of how to measure atomic number.
The periodic table of the elements is one of the most powerful tools known to science, and one which we now take for granted. Russian chemist Dmitry Mendeleev created the first true periodic table by putting the elements in order of mass. He noticed that this resulted in certain pairs of elements (for example, iodine and tellurium) being ‘back-to-front’ based on their properties, and incorrectly assumed that this was due to errors in calculating their atomic masses.
Mendeleev assigned each element an atomic number based on its position in the periodic table; however, in cases such as iodine and tellurium, this was semi-arbitrary (science-speak for ‘educated guess’) and based on chemical properties. Moseley would be the one to prove that these elements were placed correctly, based on atomic structure. He would also be the first to find experimental evidence to support the existence of atomic numbers – a concept that until then had been theoretical only.
Moseley’s speciality was X-rays. Not medical X-rays, but the study of how X-rays relate to atomic structure. I won’t go into too much technical detail, but basically what he did was to shine a beam of high energy electrons onto different metals in a vacuum. As you can see on the left, this causes the metal to emit X-rays at an angle to the electron beam. This is called diffraction.
By using a detector, Moseley could measure the angles at which the X-rays were emitted. By applying Bragg’s Law (a mathematical formula relating angle and wavelength), he could then calculate the wavelengths of X-rays given off by each metal. So far, so what? The important breakthrough came when Moseley compared wavelengths to the position of each metal in the periodic table, and found that there was a direct mathematical relationship – now known as Moseley’s Law. Finally, atomic number could be proved experimentally. Amongst other things, Moseley was able to show that Mendeleev’s positioning of problematic elements such as iodine and tellurium was correct. He was also able to solve the problem of where to put the lanthanides – in the periodic table, that is – which had been occupying chemists for years (we don’t get out much…).
In August 1914, Harry Moseley’s work was rudely interrupted by the outbreak of the First World War. In the rush of patriotism following the declaration of war, young men flocked in their thousands to enlist. Despite the efforts of his family and friends to dissuade him, Moseley felt it his patriotic duty to join them, and enlisted in the Royal Engineers. In April 1915 he was sent to Gallipoli where he served as a communications officer. On 10th August 1915, at the age of 27, one of the most brilliant young scientists of his generation was killed in action – shot by a Turkish sniper whilst relaying an order over the telephone.
The consequences to science of the loss of Moseley were significant, and his death provoked an outcry within the scientific community. Robert Millikan, who would go on to win the Nobel Prize for Physics in 1923, wrote that,
“Had the European War had no other result than the snuffing out of this young life, that alone would make it one of the most hideous and most irreparable crimes in history.”
Many scientists, including Sir Ernest Rutherford, speculated that had he lived, Moseley would certainly have been awarded a Nobel Prize for his work on atomic structure. Moseley did leave one important legacy though. His death in the First World War was a significant factor in ensuring that in the Second World War, scientific research would be designated as a reserved occupation, ensuring that scientists who would otherwise be eligible for military service were unable to enlist. Just one of many scientists whose life may well have been saved by this was Alan Turing, who made crucial discoveries in the field of computer science and played a key role in cracking the Enigma code.